The present invention is directed to amplifiers used in wireless communication systems. More specifically, the present invention relates to dual band bi-directional amplifiers for amplifying signals in two frequency bands having two uplink and two downlink frequencies.
In wireless communication systems, such as cellular telephony, bi-directional amplifiers are used to amplify signals passing in both directions between two parts of the system, such as the base station and the local service area. In the past, when the transmission signals were covered by one frequency band, a single band bi-directional amplifier having an uplink amplifier chain and a downlink amplifier chain was used to accomplish this purpose.
However, in more modern applications, bi-directional amplifiers are required to provide signal coverage in two frequency bands. Conventional dual band bi-directional amplifiers of this type have been constructed with two single-band bi-directional amplifiers connected to two power dividers. A conventional dual-band bi-directional amplifier of this type is shown in FIG. 1.
In particular, FIG. 1 shows a conventional dual-band bi-directional amplifier 100 constructed of two single-band bi-directional amplifiers 102 and 104 enclosed within the dashed boxes. Signals from the first frequency band are processed in the single-band bi-directional amplifier 102 and signals from the second frequency band are processed in the single-band bi-directional amplifier 104. Both bi-directional amplifiers 102 and 104 have the same construction.
Specifically, single-band bi-directional amplifier 102 includes uplink amplifier 110, a downlink amplifier 112, and two duplexers 114 and 116. Duplexers 114 and 116 separate the uplink and downlink frequency signals covered by the frequency band processed by the single-band bi-directional amplifier 102. Duplexer 114 passes the uplink frequency signal from a reception signal port 118 to the input of uplink amplifier 110. The output of uplink amplifier 110 is connected to the reception signal port 120 of the duplexer 116.
Likewise, duplexer 116 passes the downlink frequency signal from a transmit signal port 122 to the input of downlink amplifier 112. The output of downlink amplifier 112 is connected to the reception signal port 124 of the duplexer 114.
The single-band bi-directional amplifier 104 for the other of the two frequency bands has a similar structure.
In order to accomplish the dual-band function, the single-band bi-directional amplifiers discussed above are connected to power dividers 126 and 128 which in turn are respectively connected to antennae 130 and 132. The power dividers 126 and 128 pass the signals from the antenna into two signal paths, one for each of the two frequency bands, for the two single-band bi-directional amplifiers 102 and 104.
While this construction provides a simple solution for dual-band bi-directional signal amplification, it has a number of drawbacks. In particular, due to the power divider, the overall system gain is 6 dB lower, the output power is 3 dB lower, and noise figure is 3 dB higher. Therefore, the system sensitivity is 3 dB lower, compared to the single-band bi-directional amplifier. Furthermore, the cost of the system is greater than double the cost of a single-band bi-directional amplifier.